Extra Credit 5

Ramp: Forces and motion

Use an on-line simulation from the University of Colorado PhET group to explore the behavior of objects that are just placed on, or pushed up and down a ramp.


A free body diagram of an object on a frictionless ramp is shown above.   The y-component of the weight mg of the object is exactly canceled by the normal force of magnitude N.  The x-component of the weight accelerates the object down the ramp.

On a real ramp the object and the ramp will interact via the frictional force.  The coefficients of static friction, μs, and kinetic friction, μk, which depend on the type of surfaces that are in contact with each other, are used to calculate the maximum force of static friction and the force of kinetic friction.

fs ≤ μsN,  fk = μkN.

The frictional force always points in a direction to oppose the relative motion of the surfaces.
For the interaction between the object and the ramp fs_max = μsmg cosθ,  fk = μkmg cosθ.


Open the" Ramp:  Forces and Motion" simulation.
Link to the simulation:  https://phet.colorado.edu/en/simulation/legacy/ramp-forces-and-motion

Explore the interface!

Answer the following questions.

(a)  Place the small crate on the ramp with a ramp angle of 20o.  Click play.  Slowly increase the ramp angle.  What is the smallest angle at which the block starts to move?
Use this angle to calculate μs and compare to the given value for μs for the crate.
(b)  Place the crate on the the 30o ramp at the 8 m position.  Click play.  What is the magnitude of the acceleration of the crate, as it accelerates down the ramp?   
(c)  Place the crate on the the 30o ramp at the 8 m position.  Click play.  At what position does it come to rest?
(d)  What is the coefficients of static friction μs for the Mystery Object?
(e)  What is the coefficients of kinetic friction μk for the Mystery Object?

Now go to Canvas, Assignments, Extra Credit 5.  Answer questions 1 - 5.  You can submit twice and the highest score counts.